A continuing goal of the foamed resin or polyurethane industry is to reduce manufacturing costs. One approach that is being actively used commercially, as well as a subject of ongoing research and development is called "pour-in-place" technology. In this endeavor, the urethane foaming mixture is poured into a mold containing an upholstery material or outer layer, such as rayon, vinyl, treated natural fibers and the like. A major problem with this approach is that the reacting liquid urethane mixture can strike through or penetrate the upholstery material while the latter is conforming to the shape of the mold, and thus the shape of the desired composite article.
"Strike-through" is a problem because the reacting polyurethane mixture is poured inside the upholstery where the foaming action moves it, under pressure, toward the walls of the mold. Because of the pressure exerted on the upholstery, the urethane mixture is prone to penetrate the upholstery material and result in a defective article. Often a thin foam barrier is used in place between the foam and the upholstery. However, penetration of the foam barrier is also not preferred since even though such strike through is not visible, there is harsh feeling to the touch at the point of penetration.
Ideal pour-in-place (PIP) foams must have (1) no strike through of the fabric since this produces a defective article; (2) minimal penetration into the foam backing, preferably less than 50% of the thickness, otherwise a harsh feeling will result; and (3) no shrinkage so that the size of the article is as full as intended. In addition, there are a number of characteristics which are desirable for the PIP foam to have, namely, (4) low weight; (5) no use of chlorofluorocarbons (CFCs); (6) low cost and design flexibility; and (7) fast cure so that handling and production are easier.
A number of approaches have been developed to address the strike-through of PIP polyurethane foam systems. For example, the use of diphenylmethane diisocyanate (MDI) as the isocyanate gives foams with high initial reactivity (fast cure) and which build viscosity quickly, but such systems require chlorofluorocarbons to achieve economically viable part weights (low density) and softness. Higher catalyst contents give fast cures and minimizes penetration of the fabric, but cause shrinkage and deterioration of physical properties. Use of a thicker foam barrier stops strike through and eliminates harsh feeling, but is more costly and limits design flexibility. Another technique is to use a physical barrier film as part of the covering. This barrier film is sometimes termed a trilaminate, since the outer layer or upholstery and the thin polyurethane foam backing are counted as the other laminate layers. However trilaminate barrier films are also costly and the articles in which they are used lose breathability.
It would be advantageous if a pour-in-place polyurethane formulation could be found which did not require the use of halocarbons as blowing agents, but which did not otherwise suffer in properties from the absence of such agents. Indeed, it would be helpful to discover a PIP technology which did not require MDI as the sole polyisocyanate and/or which did not require the use of a barrier film.